Screws with coating under the head

Abstract

The invention relates to a screw (10) and to a screw assembly, comprising a screw head (11) and a screw shank (16) which projects from the underside of the screw head (11) and has a self-tapping or self-cutting thread, wherein the screw head (11) has a bearing area (12) on the underside and at least one annular groove (14) extending around the shank (16) between the bearing area (12) and the shank (16), wherein a coating (15) made of an elastic sealant is applied to the underside of the screw head (11).

Description

Technical Field

[0001] The present invention relates to a screw, comprising: a screw head; and a screw shaft, which protrudes from the lower side of the screw head and has a thread for screwing the screw into an object. Background Art

[0002] The prior art discloses a metal structural screw, wherein a washer arranged on the underside of the screw head has a coating on its underside. The coating is used to seal the surrounding area of ​​the screw head in relation to the drilled hole into which the screw is screwed, wherein the gasket on the underside of the washer abuts against the surface of the object of the screw assembly, forming a seal.

[0003] It is also known to provide a coating to a collar of a metric or imperial external thread in order to produce a screw-fastening and / or sealing mechanism together with an internal thread into which the screw is screwed.

[0004] Particularly in static metal and scaffolding construction and in the fields of structural engineering and civil engineering, fundamentally different requirements are placed on the load-bearing capacity and tightness associated with fundamentally different screw assemblies. This requires screws with self-forming or self-tapping threads, which ensure reliable strength under static loads, tightness to liquids (such as water or oil), sufficient UV resistance, simplicity and correctness in use, and the ability to be smoothly screwed in until the screw head is flat against the object, and there is contact between the assembled parts even if there is no object ready to be screwed in. Within this scope, screws provided with elastic gasket rings are known. This can achieve sufficient tightness and strength of the screw connection, but the disadvantage is that the gasket ring may be lost or forgotten and degraded by UV rays, which can lead to the intrusion of other materials and thus lose the clamping force. In addition, the sealing valve disc may be damaged or destroyed when screwed in, resulting in easy failure. In addition, the manufacturing process is complicated and costly. Summary of the invention

[0005] The invention is based on the object of specifying a screw, in particular a screw with a self-forming or self-tapping thread, which can be easily processed to produce a screw assembly and which reliably prevents the penetration of media, in particular moisture, into the bore of the screw assembly which receives the screw shank, and which minimizes the loss of initial tension and thus increases the durability of the connection. The invention is also preferably based on the object of avoiding some of the other mentioned disadvantages of existing screw designs with a self-forming or self-tapping thread and / or improving the results thereof.

[0006] The screw according to the invention should also be easy to manufacture and less expensive to produce, transport and store, and should be able to achieve a high aesthetic function, in particular when screwed in. It is also desirable that the screw according to the invention absorbs lateral pulling forces well (e.g. better than screws with sealing rings) and does not loosen on its own, is not susceptible to contact corrosion, provides a reliable seal over a long period of time, and minimizes its intrusion into other materials and / or errors in assembly.

[0007] One or more of these objects are achieved by a screw according to claim 1 and a screw assembly according to the cooperative claim 12. Advantageous developments are apparent from the dependent claims, the description and the drawings.

[0008] The screw according to the invention comprises a screw head and a screw shank, the screw shank protruding from the underside of the screw head and having a self-forming or self-tapping thread, wherein the underside of the screw head has a bearing area and an annular groove extending around the shank between the bearing area and the shank, wherein a coating made of a sealant is attached to the underside of the threaded head. The sealant is preferably elastic. Alternatively or additionally, the sealant preferably comprises a resin component of 40% to 90%, more preferably 50% to 85%, or 60% to 80% by weight, the resin component consisting of a polymeric resin or a mixture of two or more polymeric resins.

[0009] The screw assembly comprises: a screw according to the invention; a first object, such as a flat or planar object; and a second object, such as a flat or planar object, wherein at least the second object has an internal thread produced by screwing in the screw, wherein the first object is enclosed, in particular clamped, between the screw head and the second object, the thread of the screw engaging with the internal thread of the second object, and the plastic material is located between the bearing area and the first object.

[0010] The invention is based on a screw, in particular a metal structural screw, which comprises a screw head and a screw shank, which protrudes from the underside of the screw head and has a thread, in particular a self-forming or self-cutting thread.

[0011] A self-forming or self-tapping thread (external thread) is understood to be a thread which, when the screw is screwed in, produces internal thread turns by deformation of the material without removal of material or without substantial removal of material.

[0012] The screw can be designed, for example, as a self-cutting screw. A self-cutting screw is understood to be a screw which, when the screw is screwed in, produces a core drilled hole for the screw shank, in particular by removing material, i.e. pre-drilling is not absolutely necessary. The internal thread can be produced on the circumferential wall of the core drilled hole when the screw is screwed in by a self-forming or self-tapping external thread.

[0013] The screw shank can be cylindrical, for example, or can have a cylindrical portion. The thread can be formed on the cylindrical portion. Alternatively, the screw shank can taper from the screw head or slightly shorter than the screw head to the free end of the screw shank and can be formed conically in particular. The thread can extend, for example, on the screw shank, in particular on a conical or cylindrical screw shank or on a portion of the screw shank, to the screw head or slightly shorter than the screw head.

[0014] The underside of the screw head, i.e. the side of the screw shank protruding from the screw head, can have a bearing area so that the screw head rests on or comes into contact with an object, in particular a screw assembly into which the screw is screwed. Between the bearing area and the shank, the screw head has at least one annular or spiral-shaped groove extending around the shank, in particular a chip flute or an annular groove. The bottom of the groove is arranged in the screw head set back relative to the bearing area. For example, a plurality of annular grooves can be provided, which are preferably concentric relative to each other.

[0015] A coating made of a sealant and adhered to this underside is attached to the underside of the screw head.

[0016] The coating is preferably formed such that it is dry and / or feels dry to the touch and is in particular non-sticky and / or non-humid within a defined temperature range, in particular at least at room temperature. The coating thus does not wear off and remains adhered to the screw head when touched by an object or a user. This makes the screws easy to process and store, for example in the form of bulk goods. In contrast to screw processing in which a liquid sealant is applied to the screw shank only before processing, this operating step is omitted for the screws according to the invention. Preferably, the sealant according to the invention is physically dry and does not require thermal or chemical curing.

[0017] In a modification, the screw head can have a circumferential flange which protrudes in particular from the remainder of the screw head in the circumferential direction, wherein the bearing area is at least partially formed by the underside of the flange, for example completely by the underside of the flange, but preferably at least partially also by the underside of the remainder of the screw head.

[0018] Ideally, the screw head may have a screw drive profile which is suitable for cooperating with a tool in a torque-transmitting manner. Such screw drive profiles are known per se. Examples of such screw drive profiles include, for example, an outer hexagon, an inner hexagon, an outer polygon, an inner polygon, a so-called Profile, slot, cross slot, etc.

[0019] The screw shank can, for example, be perpendicular or substantially perpendicular to the support area, i.e. the support area can abut against the object into which the screw is screwed over as large an area as possible. The support area (the screw shank or its longitudinal axis, for example, is perpendicular or substantially perpendicular to the support area) can be annular or shaped as a flat ring. It can be arranged concentrically with respect to the longitudinal axis of the screw shank. The radial width of the support area can, for example, be greater than or equal to the radial width of the groove, wherein the radius is related to the longitudinal axis of the screw shank. Alternatively or additionally, the support area can be horizontal or substantially horizontal in its radial width and perpendicular or substantially perpendicular to the longitudinal axis of the support area. In other words, the surface normal of the support area, which is preferably a horizontal support area, can be parallel or substantially parallel to the longitudinal axis of the screw shank.

[0020] The bearing area can, for example, have a value A which is at least 30% of the total area TA below the screw head minus the cross section C of the (screw) shank lying in the plane of the bearing area:

[0021] A≥0.3·(TA-C) Formula 1

[0022] The value A of the support area may preferably be at least 40%, more preferably at least 50%, even more preferably at least 60% or at least 70% or at least 80%, and up to at most 90% or 95% of the total area TA below the screw head minus the cross-section C of the screw shaft lying in the plane of the support area, wherein the support area is, for example, defined by an annular groove.

[0023] It can therefore be advantageous to provide screws having an outer head diameter of 8 to 12 mm and a support width of at least 1.5 mm, screws having an outer head diameter of 13 to 20 mm and a support width of at least 2.0 mm, and screws having an outer head diameter of greater than 20 mm and a support width of at least 2.5 mm, based on commercially available rod diameters.

[0024] By way of example, it can be mentioned that for a 6-gauge screw, the value A is preferably 70% to 85%, in particular 75% to 82% or approximately 80%, of the total area TA below the screw head minus the cross-section C of the screw shank located in the plane of the supporting area; for a 10-gauge screw, the value A is preferably at least 50% to 68%, in particular 55% to 66% or approximately 63% of the total area TA below the screw head minus the cross-section C of the screw shank located in the plane of the supporting area; and for a 20-gauge screw, the value A is at least 30% to 45%, in particular 35% to 42% or approximately 40%, of the total area TA below the screw head minus the cross-section C of the screw shank located in the plane of the supporting area.

[0025] Due to the bearing area according to the invention, when the screw is tightened, the bearing pressure is distributed, thereby protecting the surface of the planar object into which it is screwed so as to maintain sealing, etc., unlike screws with a sharp-edged periphery or a conical underside of the screw head, in which all the contact pressure is pressed into the planar object through the periphery.

[0026] The screw shank can, for example, have a drilling portion provided with at least one cutting edge, preferably two circumferentially opposite cutting edges. The thread of the screw shank is formed between the at least one cutting edge and the screw head. The free end of the screw shank can, for example, form a tip having a tip angle between 90° and 170°. The at least one cutting edge can be formed in the region of the tip. The screw shank can also have a groove for each cutting edge, the groove being adjacent to the cutting edge and being formed spirally or linearly (i.e., parallel to the longitudinal axis of the screw shank), and the groove being particularly open toward the circumference of the screw shank. The at least one groove can extend only on a portion of the screw shank, wherein the thread is formed between the groove and the screw head. The groove is used on the one hand to provide a cutting surface for the at least one cutting edge, and on the other hand to accommodate chips generated by the at least one cutting edge during drilling. The tip of the screw shank can, for example, be hardened at least in the region of the cutting edge. The rest of the shank (particularly in the threaded region) can not be hardened and / or can have a lower hardness than the tip or at least one cutting edge. For example, the region of the shank in which the at least one cutting edge and / or the recess for accommodating chips is located can be formed without a thread.

[0027] The rod can for example have a portion which tapers towards the free end of the rod, which portion is particularly formed as a tip or a rounded tip, wherein the thread is formed at least partially between said portion and the screw head, wherein the tapered portion is not provided with a thread or is provided with a portion of a thread.

[0028] The thread of the rod can, for example, extend over a tapering distance until the tip. When the screw is screwed into, for example, a metal sheet that has not been pre-drilled, the thread at the tip of the screw can firmly grasp the material of the metal sheet as the screw is screwed in and pull the screw into the metal sheet.

[0029] Alternatively, the tapered portion may not be formed with a thread, in particular for forming a friction drill hole. In the region of the tip or tapered portion, the rod may, for example, be formed with a non-circular or approximately polygonal or elliptical cross section, or alternatively a circular or round cross section. The tip adjacent to the tapered region may preferably be rounded.

[0030] The coating can be arranged in and in particular adhere to at least the region of the bearing region. Optionally, the coating can also be arranged in the region of at least one groove (chip groove) and / or in the region of the rod. The coating can be arranged in at least one annular groove and can also span annular grooves. The coating can cover an area on the rod, in particular a partial area on the rod, which preferably includes at least one turn of the thread, particularly preferably at least two turns or three turns. It can preferably be limited to a maximum of eight turns or a maximum of six turns and / or a maximum of four turns or even three turns of the thread.

[0031] When the screw is screwed into one or more objects to form a screw assembly, the underside of the screw head together with the coating arranged thereon is pressed against the object, thereby sealing a radially outer region of the coating relative to a radially inner region of the coating and / or a region of the screw assembly which the screw shank is screwed into. The seal can be further improved or strengthened if the coating also adheres in the region of the annular groove and / or to the screw shank.

[0032] The at least one groove serves to receive material of the object into which the screw is being or will be screwed. By screwing the screw into the object, burrs or at least one chip are generated around the threaded bore, which prevents the bearing area from resting as fully as possible on the object and thus impairs the sealing effect. The annular groove serves to receive this burr or at least one chip, if it has not been ejected during the screwing process, so that the coating of the bearing area can lie against the object and form a reliable seal.

[0033] In a refinement, when the screw is not screwed in, the layer thickness of the coating can be at least 0.1 mm, preferably at least 0.2 mm, most particularly preferably at least 0.4 mm, and in particular at most 0.9 mm, preferably at most 0.8 mm, most particularly preferably at most 0.7 mm, for example, at least on the underside of the bearing area, in particular on the outside of the groove area, 0.4-0.6 mm. When the screw is screwed in, if only the surface roughness is filled, the layer thickness can be reduced to 0 mm. For when the screw is screwed in, a layer thickness in the range of 0.01-0.4 mm, in particular 0.1-0.2 mm is preferred. It has been found that these layer thicknesses enable an optimal sealing effect to be achieved while saving material for the coating.

[0034] The invention also relates to a screw assembly comprising a screw according to the invention and a first object and a second object. At least the second object can have an internal thread produced by screwing in the screw, wherein the first object is enclosed, in particular clamped, between the screw head (in particular the underside of the screw head) and the second object. Optionally, the first object can also have an internal thread. The thread of the screw engages with the internal thread of the second object, and the plastic material and / or the coating is located between the bearing area and the first object.

[0035] The first object may be, for example, flat or planar and in particular formed as a plate or metal sheet. The first object may be, for example, formed of metal (including metal alloys), wood or plastic or a composite material, in particular a composite material made of these materials. The surface facing the screw head is preferably smooth or at least tempered so that the coating on the underside of the screw head seals the contact gap between the surface and the coating. The surface may be formed, for example, by a metal or plastic layer formed by or on the first object.

[0036] The second object may be flat or planar, for example, and in particular formed as a plate or metal plate.The second object may be formed, for example, from metal (including metal alloys), wood or plastic or a composite material, in particular a composite material made of these materials.

[0037] The two metal plates (corresponding to the first and second objects) can be connected, for example, by screws according to the invention. In another example, the metal plate corresponding to the first object can be attached to the second object made of wood or plastic. The above examples are to be understood only as examples, and other combinations of the first object and the second object are not excluded.

[0038] In particular, when forming the screw assembly, the coating can be deformed, in particular its layer thickness can be reduced. The material of the coating can, for example, flow, in particular radially outwards and / or radially inwards (i.e. towards the rod), in particular into the annular groove. By pressing the screw head against the first object, the coating or at least a part thereof can, for example, be deformed elastically and / or plastically so as to form a bead on the outer edge of the screw head that partially or completely surrounds the screw head.

[0039] The coating held between the bearing area and the first body reliably seals the radially outer area of ​​the bearing area relative to the radially inner area of ​​the bearing area or the threaded bore. The material can also leave the bearing area of ​​the head and enable contact between the parts to be connected; this enables high durability and, by filling in surface roughness, a reliable seal against the surrounding medium.

[0040] The partially or fully circumferential bead formed by the radially outwardly displaced coating provides an even better seal. The bead also protects the portion of the coating between the underside of the screw head and the first object, for example from UV radiation from the sun, thereby further improving the durability of the seal and preventing or reducing the intrusion of other materials.

[0041] In one embodiment, the first object may have a through hole, in particular a hole produced by drilling or punching or in some similar manner, the diameter of which is greater than the outer diameter of the outer thread of the screw shank, and through which the screw shank extends. In such an embodiment, the screw does not need to be threaded in the first object.

[0042] In an alternative embodiment, the first body can have an internal thread which is produced by screwing in a screw, wherein the thread of the screw engages with the internal thread of the first body, in particular also with the internal thread of the second body.

[0043] The sealant attached to the underside of the screw head can preferably be elastic. In particular, the sealant can be elastic over the entire range between -10°C and +100°C, in particular between -40°C and +150°C.

[0044] Elasticity refers to the property of a polymer to reversibly return to its initial state after deformation, where the initial state is entropically more favorable than the stretched state in which the polymer chains are arranged in parallel (more disordered as a "wad"). Rubber elasticity in polymers generally occurs in the temperature range between the glass transition temperature and the decomposition temperature (elastomers) or softening temperature (crystalline and partially crystalline thermoplastics). In contrast, the sealants used according to the invention are capable of both elastic and plastic deformation under screw-in conditions.

[0045] The sealant and in particular its resin component is preferably elastic at least in a range, preferably at least in the entire range of -10°C to +100°C, more preferably also above 130°C or even preferably up to 200°C. The sealant and in particular its resin component is preferably elastic down to -30°C or even -40°C. It is preferably dry to the touch and non-sticky and non-wet at room temperature and standard pressure or under processing conditions, for example, between -10°C and +50°C, even up to 100°C or 130°C or even 200°C. A person skilled in the art will understand that "dry to the touch" refers to the state of a coated part in which no appreciable amount of material is transferred when touched by hand or with an absorbent material.

[0046] The person skilled in the art will understand that the "non-stick" property means that the cohesion of the sealant is always higher than the adhesive force relative to the adjacent material (such as, for example, a hand or a glove, etc.). In this way, the sealant does not form threads, is satisfactory to use, and the layer thickness is not changed in particular by normal working conditions (such as being clamped, stored or the like). The strength of the polymer at room temperature (23°C) is preferably 2 N / mm 2 Up to 10N / mm 2 .

[0047] According to the invention, the sealant may contain in particular 40 to 90% by weight of a resin component, said numerical component consisting of one polymer resin or of a mixture of two or more polymer resins, wherein, if there is one resin, it is preferably elastic, and if there are a plurality of polymer resins, they are preferably elastic or include one or more elastic resins.

[0048] The sealant may, for example, and preferably is, a non-reactive sealant; the resin component preferably consists of one or more non-reactive polymer resins.

[0049] Therefore, the resin component of the sealant is particularly preferably non-reactive. Those skilled in the art will understand that non-reactive polymer resins refer to polymers that are not chemically cured in order to achieve their sealing and / or adhesion functions. Suitable non-reactive polymer resins include, for example, acrylates, acrylate copolymers, polyolefins, silicones, plastisols, polyamides, polyvinyl chloride (PVC), acrylonitrile / chlorinated polyethylene / styrene, butadiene rubber, chloroprene rubber, ethylene-propylene copolymers, ethylene-propylene-diene-(monomer) rubber terpolymer EPDM, ethylene vinyl acetate, fluororubber, isoprene rubber, natural rubber, polyether block amides, polyhydroxyalkanoates, polyhydroxybutyrates, polyisobutylene, polyurethane, polyvinyl alcohol, styrene butadiene rubber, styrene butadiene styrene, vinyl chloride / ethylene. Most preferably, acrylates and acrylate copolymers. Examples of particularly suitable acrylate copolymers include: acrylonitrile / butadiene / acrylate, acrylonitrile / methacrylate, ethylene ethyl acrylate copolymers, vinyl chloride / ethylene / methacrylate. In contrast, for example, polymethyl methacrylate is not a preferred polymer resin as the resin component due to its lack of elasticity.

[0050] The resin component of the sealant preferably includes one or more acrylate polymers and / or one or more acrylate copolymers; in particular, the resin component may preferably consist of an acrylate polymer and an acrylate copolymer.

[0051] For example, silicones are not preferred due to their relatively low elongation at break. For example, polyolefins are not preferred due to their low temperature resistance, especially with regard to their dimensional stability and / or chemical resistance. Plastisols (uncured and cured) are not preferred, at least due to the plasticizers they contain and their reduced durability and environmental compatibility due to leaching. Polyamides, polyvinyl chloride and other polymeric sealants are also not preferred because of their low elasticity and elongation at break. Polyurethanes are not preferred because of their lack of stability and high invasiveness to other materials.

[0052] However, the sealant according to the invention, in its most general terms but not preferably, may also be a touch-tight and dry-curing polymer, such as a thermosetting polyurethane.

[0053] Ideally, the sealant may consist of a single component which is easy to apply and non-curing, in particular non-thermosetting, wherein the sealant may preferably be applied as a dispersion, in particular an aqueous dispersion, and then dried to a constant weight.

[0054] The sealant dispersion for application preferably contains additives such as inorganic and / or organic dyes or pigments (whose particle size is generally limited to a median of 1.5 to 6 μm, preferably 2 to 4 μm), wetting agents, brighteners, solubilizers, fillers (whose particle size is generally limited to a median of 1.5 to 6 μm, preferably 2 to 4 μm), defoamers, ionic and / or non-ionic thickeners, corrosion inhibitors, antioxidants, friction modifiers, lubricants and / or rheological additives.

[0055] In a preferred embodiment, the sealant may be applied as an aqueous dispersion, wherein the aqueous dispersion comprises:

[0056] 30 to 80% by weight, preferably 40 to 70% by weight, in particular 50 to 60% by weight of an aqueous resin dispersion;

[0057] 15 to 55% by weight, preferably 20 to 50% by weight, in particular 30 to 40% by weight of additives;

[0058] 5 to 30% by weight, preferably 7 to 20% by weight, in particular 10 to 15% by weight, of water.

[0059] For example, the dispersion to be applied may have the following composition:

[0060] 15% to 20% by weight of an aqueous high solids dispersion (60% to 65% solids) of a highly elastomeric acrylate copolymer having a glass transition temperature below -10°C;

[0061] 35% to 42% by weight of an aqueous high solids dispersion (60% to 65% solids) of a highly elastomeric acrylate polymer having a glass transition temperature between 5°C and 15°C;

[0062] 5 to 15% by weight of an aqueous dispersion of a lubricant (e.g., wax; particle size of at least 98%)

[0063] <8.5μm, median between 2-4μm; wax drop point 100℃ to 130℃, 40% to 50% solids);

[0064] 2% to 8% by weight of an inorganic pigment paste in water (47% to 55% solids);

[0065] 10% to 15% by weight of fillers (e.g., inorganic carbonates);

[0066] 5% to 10% by weight of other additives (such as wetting agents, brighteners, solubilizers, defoamers, thickeners);

[0067] The rest is water.

[0068] In the dispersed state, the sealant is easy to process and viscous; the dynamic viscosity at room temperature (22° C.) according to DIN 53211: 1987-06 and DIN 2431: 2020-02 (measured using an Anton Paar MCR 92 rheometer) may be in the range of 12000-1300 mPa·s at 1 rpm, in particular 8000-1800 mPa·s or even 6000-2300 mPa·s; in the range of 900-100 mPa·s at 100 rpm, preferably 800-125 mPa·s, in particular 650-150 mPa·s or 500-175 mPa·s; and in the range of 500-25 mPa·s at 1000 rpm, preferably 450-35 mPa·s, in particular 350-50 mPa·s or 250-65 mPa·s, each particularly preferably:

[0069] rpm Viscosity (mPa·s) 1 1800 100 150 1000 50

[0070] or:

[0071] rpm Viscosity (mPa·s) 1 8000 100 650 1000 350

[0072] Once dried, the sealant is preferably dry to the touch, no longer soluble or dispersible in water and is preferably amorphous. The sealant according to the invention preferably has "super-tough" properties in addition to elastic properties. Super-tough materials not only deform elastically under pressure, but also deform plastically. It "flows" so to speak so as to get into available flutes, cracks, grooves and cavities, while materials that are not super-tough (such as, for example, cured thermosetting plastics, including active sealants or adhesives) will break under pressure. For example, "super-tough" materials are understood to be those materials that have an elongation at break of 150% to 250% in a high-speed tensile test at 200 mm / min according to ISO 18872:2007-02 and ENISO 527-1:2019-11. Therefore, the sealant according to the invention preferably exhibits an elongation at break of in particular 170% to 230% or ideally 180% to 200%. Alternatively, a sealant may be referred to as "super-tough" if, in a test for determining the breaking torque and the prevailing torque (according to DIN 267-27), the prevailing torque measured at 100° of rotation is still at least 80% of the breaking torque, preferably at least 90% of the breaking torque, most particularly at least 100% of the breaking torque, wherein the material does not change its structure and / or is not destroyed, so that even after typical curing times (e.g. 24 hours) the test can be repeated with similar values ​​and no breaking torque peak is reached.

[0073] For example, the sealant may have a Shore hardness of 20 to 100, in particular 20 to 90 or 30 to 50, in particular 40±5, measured according to DIN EN ISO 868:2003-10.

[0074] The applied sealant, which is dry to the touch, preferably has very good adhesion. In an adhesion test on a flat steel surface according to DIN EN ISO 2409:2013-06, preferably at least good adhesion (1 out of 4) is achieved, with damage along the cut edge of at most 5%.

[0075] The pre-applied sealant of the invention eliminates for the first time the need for additional sealing means such as "O-rings" or sealing disks (e.g. conventional EPDM sealing disks) and the associated risk of error with common screws such as structural screws. The seal produced according to the invention is durable due to its resistance to temperature, water and chemicals (e.g. oils, alcohols, gasoline, organic solvents) and acidic or alkaline environmental influences. It is dimensionally stable, in particular when a non-reactive and / or non-hardening sealant is used.

[0076] For example, the temperature resistance of the sealing effect of the sealant can be determined according to the method of DIN 267-27:2009-09, which specifies aging for 1000 hours at 20° C., 100° C., 150° C., 170° C. and 200° C. and room temperature as the test temperature. Preferably, no leakage is detected in the sealant used according to the invention.

[0077] For example, the chemical resistance can be determined according to the method of DIN 267-27:2009-09. Preferably, the sealant used according to the invention has no detectable leakage within 10 minutes in a test below 6 bar after 7 days of exposure to various liquid media (e.g. 100% ethylene glycol, 1:1 water / ethylene glycol mixture).

[0078] Adhesion and cohesion values ​​can be expressed by determining the assembly torque according to DIN 267-28:2009-09. Assembly torque M ass Preferably in the range of 2 to 10 Nm, particularly preferably 3 Nm to 7 Nm (based on ISO 4017 M10x35-8.8-black oxide screws and ISO 4032 M10-10-black oxide nuts, tested according to DIN 267-28:2009-09).

[0079] The UV resistance of the sealant can be tested under artificial UV light ( UV lamp UV-250 (G spectrum), intensity 30mW / cm 2Preferably, after two weeks of irradiation, the sealant used according to the invention has no measurable change in Shore hardness, elasticity or elongation at break and / or tear strength.

[0080] In addition to being coated with a sealant, the screw according to the invention can also be coated with a reactive adhesive, such as a two-component adhesive, which is dry to the touch. Without the need for an additional adhesive coating, the screw according to the invention can be well suited for repeated use. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] The invention has been described on the basis of a number of embodiments and examples. The embodiments are described below based on the drawings. The features disclosed thus advantageously develop the subject matter of the claims, both individually and in any combination of features. It is shown that:

[0082] Figure 1 is a side view of a screw according to the present invention;

[0083] Figure 2 is a screw assembly comprising a first and a second planar object and a Figure 1 screws. DETAILED DESCRIPTION

[0084] Figure 1 and Figure 2 The screw 10 in the embodiment has a screw head 11 and a screw shaft 16 extending from below the screw head 11. The underside of the screw head 11 has a support area 12 for supporting an object 20 ( Figure 2 ). The screw head 11 has a flange 13 which is circumferential on the outer circumference of the screw head 11 and projects radially outwards relative to the rest of the screw head 11. The bearing area 12 is formed by the underside of the screw head 11, a part of which is formed by the flange 13. The screw head 11 has a screw drive profile which is suitable for cooperating with a tool in a torque-transmitting manner. In particular, a screw shank 16 which projects perpendicularly or normally from the bearing area 12 has an external thread, in particular a non-metric external thread, via which the screw 10 can be screwed into at least one object 20, 30.

[0085] The screw shank 16 has a substantially cylindrical portion, wherein at least the cylindrical portion has an external thread 17. In the example shown, the side of the screw shank 16 that projects from the cylindrical portion has a tapering, in particular conically tapering portion, which forms a tip at the free end of the screw shank 16. In the example shown, the thread 17 extends not only over the cylindrical portion of the screw shank 16, but also over the tapering portion of the screw shank 16, up to or almost to the tip.

[0086] The thread 17 is formed as a self-tapping or self-forming thread. The screw 10 can be screwed into the object 20, 30 without the need for a core hole or any drilling.

[0087] The screw 10 is preferably provided or designed to be screwed into a thin planar object, such as a metal sheet. Two metal sheets or objects 20, 30 can be connected by means of the screw 10 to form a screw assembly ( Figure 2 ).

[0088] The support region 12, in particular the horizontal support region 12, surrounds the screw shank 16 in an annular manner or in the shape of a flattened annulus. An annular groove 14 is arranged between the support region 12 and the screw shank 16, which is formed as a chip groove or notch in the example shown. The groove 14 delimits the support region 12 towards the screw shank 16 (i.e. radially inwardly), which region is particularly formed as a circular annular surface. The outer circumference or flange 13 of the screw head 11 delimits the support region 12 radially to the outside. The bottom or base of the groove 14 is embedded in the screw head 11 relative to the support region 12. The flanks of the groove 14 preferably transition to the bottom or base of the groove 14 in a rounded manner. Notch effects in the groove 14 are thus advantageously avoided.

[0089] The coating arranged on the underside of the screw head 11 partially or completely covers at least the bearing area 12. In the example shown, the coating 15 also spans the groove 14 and also partially extends onto the screw shank 16, in particular the cylindrical part of the screw shank 16, as shown by reference numeral 18. In the area 18, the coating 15 preferably extends over at least one, two or three turns of the thread, up to and including all turns. However, in some embodiments, the coating preferably does not extend over all turns, but for example only extends over one, two or three turns of the thread. In the exemplary embodiment shown, the area 18 extends over two turns of the thread. The tapering part of the screw shank 16 preferably does not include the coating 15.

[0090] The coating 15 is implemented as a preferably elastic sealant. The sealant is particularly elastic between -10°C and +100°C, preferably over the entire range. The coating 15 is preferably implemented so that it is firm to the touch, i.e., non-sticky to the touch. This allows the screws to be stored and handled as bulk goods, wherein it can be added that the screws do not necessarily have to be provided as bulk goods, but can also be provided in different forms, for example in so-called screw making machines.

[0091] Figure 2 The screw assembly shown includes a Figure 1 The screw 10 or another variant of the screw according to the invention, the first planar object 20 and the second planar object 30. Figure 2In the example of the embodiment of the present invention, the first object 20 and the second object 30 have an internal thread formed by screwing the screw 10 therein, wherein the first object 20 is enclosed or sandwiched between the screw head 11 and the second object 30. When the screw assembly is completed, the external thread 17 of the screw 10 engages with the internal thread of the first object 20 and the second object 30. The underside of the screw head 11 is supported by the bearing area 12 provided with the coating 15 on the top side of the first object 20, i.e., the side or surface of the first object 20 facing the screw head 11. By tightening the screw and increasing the contact pressure or contact force of the screw head 11 on the first object 20, the coating 15 is at least partially displaced from the gap between the bearing area 12 and the top side of the first object 20, in particular radially outwards (i.e., towards the outside of the screw head 11) and / or radially inwards (i.e., towards the shaft 16 and / or the groove 14). The coating 15 remaining between the bearing area 12 and the first body 20 seals the area outside the screw head 11 related to the threaded borehole in which the screw shank 16 is located, in particular in an airtight and / or liquid-tight manner. The portion of the coating 15 displaced radially outwards can form a bead 19 around the screw head 11.

[0092] The groove 14 is used to accommodate a burr, which is formed, for example, by screwing the rod 16 into the first object 20 and which protrudes beyond the top side of the first object 20. The groove 14 is also used to accommodate some of the coating 15. The groove 14 thus ensures that any burrs present do not or do not substantially impair the sealing effect between the support area 12 and the top side of the first object 20. Alternatively or additionally, the material of the coating 15 accommodated in the groove 14 or displaced into the groove 14 can even produce a sealing effect in the groove 14, in particular using a burr or at least one chip that may be present. This further improves the sealing effect.

[0093] The coated sealant 15, due to its plastic and elastic properties when screwed in, is well suited to exhibit a certain flow behavior, so that the sealant substantially fills the surface roughness between the bearing area 12 and the top side of the first body 20, thereby contributing to the sealing function. The displacement of material to the side not affected by the load and thus filling the entire thread gap can also improve the sealing. In addition, the sealant is preferably able to form an additional bead (not shown) at the periphery of the surface, thereby achieving an additional gasket function.

[0094] The coating 15 or the coating 18 optionally provided on the shank 16 can seal the area between the inner diameter of the internal thread of the first body 20 and / or the second body 30 and the outer diameter of the screw shank 16, in particular the cylindrical portion. Any material of the coating 15 that is displaced by the screw shank 16 when the screw 10 is screwed into the first body 20 and the second body 30 can in particular be displaced into the groove 14 and / or be accommodated in the groove 14.

[0095] As an alternative to the through-hole of the screw shank 16 which is produced by screwing the screw 10 into the first body 20 , the first body 20 has a through-hole whose diameter in the region of the cylindrical part of the shank 10 is greater than the outer diameter of the thread 17 .

[0096] Example 1

[0097] according to Figure 1 Comparative screws were produced and coated with a different sealant having a thickness of 0.5 mm on the underside of the bearing area outside the groove, wherein the sealant also covered the groove and the adjacent shank up to and including two thread turns.

[0098] The sealant compositions were tested as aqueous dispersions and contained either elastic acrylates or polyamides or non-elastic acrylates or polyurethanes as sealants. Alternatively, EPDM seals were also tested. The best threaded connection tightness and strength were achieved with elastic sealants containing elastic acrylates.

[0099] The screws coated with elastic acrylate according to the invention also proved to be superior to otherwise identical screws (which were provided with an EPDM sealing ring). The screws coated according to the invention achieve good sealing values ​​even at tightening torques that press against the EPDM disk and thus destroy its sealing effect, and also withstand relative movements better than EPDM.

[0100] Example 2

[0101] The following comparative tests between an ultra-tough and elastic acrylate-based sealant used in accordance with the present invention and a non-elastic, anaerobic curing (ie, reactive) acrylate adhesive were also conducted.

[0102] In order to demonstrate the difference in fracture behavior between the sealant used according to the invention and the anaerobic curing acrylate adhesive by the example of two adhesive surfaces bonded using an anaerobic curing acrylate adhesive, two metal strips were coated and bonded with Loctite 577 and Weicon AN 306-01, respectively. As an example according to the invention, an elastic and super-tough acrylate-based sealant was also attached between the two metal strips.

[0103] The metal strip laminates were clamped with screws and tested for fracture behavior / toughness, wherein it was found that the sealants used according to the invention exhibit elastic behavior with the desired adhesion and cohesion and in particular superior toughness, whereas the anaerobically curing acrylate adhesive was very hard and failed suddenly.

[0104] Example 3

[0105] In another comparative test, the adhesion / cohesion between a screw and a flat object was investigated. It was found that in the case of a screw coated under a head according to the invention, the elastic supertough sealant "flowed" into all gaps and asperities when pressed, and was partially pushed out of the gaps, where it felt firm to the touch and dried immediately; whereas the anaerobic hardening adhesive could only be applied in a thin layer and only cured where there was no oxygen. All material that was pushed out of the gaps did not cure, but remained sticky and wet.

[0106] We also measured the Acrylic Adhesive / Sealant( The breaking torque of screws with the same coatings (561, 577 and 511) was compared with the breaking torque of the same screws coated with a non-reactive elastic acrylate-based sealant according to the present invention. The screws coated with the invention exhibited a sharp breaking torque, which was reflected by a torque peak at about 10° and then a rapid decline (less than 50% of the breaking torque was always measured at 20°), while the screws coated according to the invention exhibited a clear dominant torque and maintained a breaking torque of significantly more than 50% even at 300°. Even after 24 hours, the sealant of the screws coated according to the invention retained its toughness.

[0107] Example 4

[0108] Anaerobic curing (ie, reactive, non-elastic) adhesives cannot be pre-coated, as shown in the following comparative tests.

[0109] One screw was coated with an ultra-tough, elastic, acrylate-based sealant, while the other two screws were coated with an anaerobic-curing, non-elastic, acrylate-based sealant / adhesive.

[0110] The paper smears show that a coating that is dry to the touch and firm and can be pre-coated is only achieved according to the invention. If the corresponding coated screw is screwed in immediately after coating, it can also be found that the screw according to the invention is firm to the touch from the first seconds after screwing in. The dry to the touch and firm sealant pressed out from under the screw head still has elastic and super-tough properties and retains these super-tough and elastic properties even after mechanical tests. In contrast, anaerobically curing acrylate sealants that appear in liquid form can still be applied 24 hours after screwing in.

[0111] Reference numerals list

[0112] 10 Screws

[0113] 11 Screw head

[0114] 12 Support area

[0115] 13 Flange

[0116] 14 Grooves, especially chip grooves or annular grooves

[0117] 15 Coating

[0118] 16 Screw rod

[0119] 17 External thread

[0120] 18 Section of coating 15 in the area of ​​screw shaft 16

[0121] 19 Beaded Edge

[0122] 20 A flat or planar first object, especially a metal plate

[0123] 30 A flat or planar second object, in particular a metal plate.

Claims

1. A screw (10), comprising: A screw head (11) and a screw shank (16), the screw shank (16) protruding from the underside of the screw head (11) and having a self-forming or self-tapping thread (17), wherein the underside of the screw head (11) has a bearing area (12) and at least one annular groove (14), the groove extending around the screw shank (16) between the bearing area (12) and the screw shank (16), wherein a coating (15) made of an elastic non-reactive sealant is attached to the underside of the screw head (11), characterized in that the sealant includes, as a resin component, one or more acrylate polymers and / or one or more acrylate copolymers, and the screw shank (16) is perpendicular or substantially perpendicular to the bearing area (12), so that the bearing area can abut against the object into which the screw (10) is screwed over as large an area as possible.

2. The screw (10) according to claim 1, characterized in that The screw shank (16) has a drilling portion provided with at least one cutting edge, wherein the thread (17) is formed between the drilling portion and the screw head (11).

3. The screw (10) according to claim 1, characterized in that: The screw shank (16) has a portion which tapers towards the free end of the screw shank (16), wherein the thread (17) is at least partially formed between the tapered portion and the screw head (11), wherein the tapered portion has no thread (17) or has some thread (17).

4. The screw (10) according to claim 3, characterized in that The screw shaft (16) is formed into a pointed end or a rounded pointed end.

5. The screw (10) according to claim 1, characterized in that The layer thickness of the coating (15) outside the region of the groove (14) is between 0.1 mm and 0.9 mm.

6. The screw (10) according to claim 1, characterized in that The sealant includes 40 to 90% by weight of a resin component consisting of a polymer resin or a mixture of two or more polymer resins.

7. The screw (10) according to claim 6, characterized in that The resin comprises or consists of one or more elastic resins.

8. The screw (10) according to claim 1, characterized in that The resin component of the sealant consists of an acrylate polymer and an acrylate copolymer.

9. The screw (10) according to claim 1, characterized in that The sealant exhibits an elongation at break of 150% to 250% in a high speed tensile test at 200 mm / min according to ISO 18872 and EN ISO 527-1.

10. The screw (10) according to claim 1, characterized in that The sealant exhibits an elongation at break of 170% to 230% in a high speed tensile test at 200 mm / min according to ISO 18872 and EN ISO 527-1.

11. The screw (10) according to claim 1, characterized in that The sealant, which includes one or more acrylate polymers and / or one or more acrylate copolymers as a resin component, also covers an area (18) on the screw shaft (16).

12. The screw (10) according to claim 11, characterized in that The region (18) comprises at least one turn of the thread.

13. A screw assembly, comprising a screw (10) according to any one of the preceding claims, a first object (20), and a second object (30), wherein at least the second object (30) has an internal thread produced by screwing into the screw (10), wherein the first object (20) is sealed between the screw head (11) and the second object (30), the thread (17) of the screw (10) is engaged with the internal thread of the second object (30), and the sealant of the coating (15) is located between the bearing area (12) and the first object (20).

14. The screw assembly according to claim 13, characterized in that The first object (20) has an internal thread produced by screwing the screw (10), wherein the thread (17) of the screw (10) engages with the internal thread of the first object (20).

15. The screw assembly according to claim 13, characterized in that: The first object (20) has a through hole, the diameter of which is larger than the outer diameter of the thread (17), and the screw shaft (16) extends through the through hole.

16. The screw assembly according to claim 13, characterized in that A bead (19) surrounds the screw head (11).

17. The screw assembly according to claim 16, characterized in that The bead (19) is formed by some of the coating (15).

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